publish v2.3.1 patch

Author: Jeongho Nam

package.json

@@ -6,7 +6,7 @@
     "email": "[email protected]",
     "url": "http://samchon.org"
   },
-  "version": "2.3.1-dev.20191212",
+  "version": "2.3.1",
   "main": "./index.js",
   "typings": "./index.d.ts",
   "scripts": {